This invention relates to using the expansion force of an air spring, coupled between a snowplow vehicle and the attached snowplow, so that contact between the ground engaging components of the snowplow, and the road can be controlled, either automatically or manually.
Air springs have long been known, and are widely used in vehicle suspension systems, and have been adapted to other applications as well.
A weight transfer system is disclosed in U.S. Pat. No. 4,314,709 using an air bag, to transfer load from a vehicle to an auxiliary axle thus reducing weight on the main chassis wheels. (Air springs were once referred to as air bags but now the term xe2x80x9cair springxe2x80x9d is preferable, to distinguish them from air bags now commonly placed in steering wheels for crash protection)
They have also been used as a means to control tension, as in Canadian Patent CA 1,203,420. A baling machine is disclosed, having a piston moving longitudinally on guides, with the piston displacing air in a air spring as it moves to and fro, rigidly connected to an arm assembly.
U.S. Pat. No. 5,060,334 shows a street sweeper, having air spring means, to control the amount of sweeping pressure a rotary broom exerts on a surface. The system uses a pivot beam with an adjustable air spring at one end of the beam and a boom attached on the other end. As the air spring expands, the beam pivots, lifting or lower the broom.
Air springs have also been adapted to raising and lowering a snowplow scraper blade. As disclosed in U.S. Pat. No. 6,324,775 the operator may vary the air pressure in alternate sets of air springs. By varying the pressure, the amount of force the scraper blade exerts on a surface may be varied. This system requires multiple air springs, and is not suitable for implement attachments which must be quickly removed.
As well the air spring used must be very large to raise a relatively light blade. As disclosed in FIG. 3, frame 17 has no guide means to ensure it remains at right angles to the truck frame, as it is urged upwards in response to air pressure, and thus will tend to cock forward or rearward, as pressure is added to the air spring, greatly reducing its longitudinal force.
Large highway snowplows mounted at the front of a drive vehicle weigh approximately 2,000 pounds, and this weight must closely follow the contour of the road, independent of the drive vehicle. Steel skid-shoes have been, for years, the common means to support a large portion of the weight of the plow.
The normal set-up is to adjust the skid-shoes at approximately the same horizontal plane as the blade, and are adjusted or replaced as the skid-shoes and blades wear out. The plows have become heavier over the years and plowing speeds much faster, resulting in rapid wear. The snowplows blades and shoes normally last for about 8 hours of plowing, before they must be replaced or adjusted. The costs of the blades as well as the skid-shoes, add considerably to the cost of snow removal. As well there is the labour cost to change components, and down-time.
Another problem associated with steel skid-shoes, is the tremendous vibration and road shock they transfer, from the rough road surface to the main body of the snowplow. The jar from every crack and pot-hole is transmitted directly to the plow, resulting in continual breakage, and cracks to the main structure.
Various methods have been used over the years to extend the life of the blades and skid-shoes. Canadian Patent CA 1160043 discloses skid-shoes having carbide inserts, and Canadian Patent CA 2153408 discloses a flexible blade having hardened inserts.
Castor wheels have been used to carry the weight of the plow; however, they can cause vehicle directional control problems. They tend to have a xe2x80x9cshopping cart effectxe2x80x9d with wheel wobble becoming more pronounced as speed increases.
Wheels fixed in a straight ahead position have been tried, in order to eliminate this problem, however, on slippery roads can cause the dangerous situation of the snowplow steering the vehicle straight ahead when the operator wants to turn.
U.S. Pat. No. 5,265,356 discloses a hydraulic system to regulate the friction between the blade and the road, thus reducing wear. Hydraulic systems, however, are heavy, expensive and complicated to repair and maintain. Also in operation, do not respond quickly enough to the rapidly changing pressure requirements of a snowplow vehicle travelling down the road at 60 KPH.
A mechanical spring device used to control the amount of force an implement attachment exerts on the ground is disclosed in U.S. Pat. No. 5,285,856, which uses a steel cylinder supplied with compressed air, to control the amount of force sugar cane piler tips exert on the ground. To transfer larger weights, however, a steel cylinder of great size and weight is required when using compressed air, which normally operates at a maximum pressure of 130 psi.
Air springs in general are defined as fabric-reinforced rubber bellows, sealed with bead plates, containing a column of compressed air. An air fitting, located in one of the bead plates allows fluid to flow in and out of the bellows. The bead plates also normally have means of bolting the air spring to what ever the air spring is sandwiched between. The air spring is designed such that fluid pressure expands the diameter of the air spring very slightly, while longitudinal expansion is approximately 8 inches for a medium air spring having a diameter of 9 inches. As long as the two bead plates are parallel as the air spring expands, and the expansion is along a straight line, when sandwiched between two members, the longitudinal expansion force of the air spring will tend to force the members apart. However, if parallel alignment is not maintained between the members, and the air spring is allowed to bend as it expands, than longitudinal force pressing against the members will be reduced.
It would be highly desirable to provide a simple means of coupling an air spring directly to a means of force transmission such as cable or chain, so that the expansion force of the air spring could transfer weight from an attached implement to the vehicle.
An air spring actuator, sandwiching an air spring between its interlinked members is disclosed, connecting between a snowplow and the drive vehicle, so that longitudinal expansion of the air spring causes tension, transferring weight from the snowplow to the drive vehicle. One member of an air spring apparatus is mechanically attached to the front push-frame of a snowplow vehicle, while a second moveable member slides longitudinally in guide slots of the attached member, with an air spring sandwiched between the two members. The moveable member can be connected to the snowplow by any mechanical means of force transfer, but flexible means, such as cable or chain are particularly advantageous.
A cable connected to the moveable member travels over a sheave, out over another sheave supported by a boom structure mounted on the front of a push frame, to a desired lift point above the plow, and then coupled at a balance bar, welded to the lower side of the plow""s push-frame, such that the weight of the plow is horizontally balanced between the skid-shoes of the snowplow.
The air pressure and thus the amount of cable tension are infinitely adjustable, between zero and the amount of pressure in the vehicle""s air pressure reservoir.
The cable is attached to the snowplow at a point approximately two feet from the plow vehicle, while the plow extends forward another six to eight feet. Therefore one inch of vertical movement of the cable causes approximately three inches of vertical movement of the snowplow cutting edge. In addition, the cable is connected at the plows horizontal balance point by a single pin, ensuring that the plow will follow a horizontal plane, so that while tension is maintained on the cable, the snowplow can still follow the ups and downs of the road. When the vehicle travelling down the road encounters a dip, the plow begins to drop, increasing the tension on the cable, which in turn increases air pressure in the air spring. The extra pressure is released to atmosphere by a relieving regulator, returning the system to its pre-set pressure.
Conversely when the plow encounters a rise, the plow is forced up, tension is reduced, air spring pressure drops, and the regulator opens to allow more air pressure to enter the air spring, and the system again returns to it""s pre-set pressure. Thus the invention, when properly adjusted, will enable the snowplow vehicle to travel over an uneven surface and still maintain contact, but with reduced wear.
It should be noted that the snowplow weight transfer system in no way interferes with the plow lift system. However, the operator must ensure that the plow lift chains are slack enough when the system is in operation so that they remain slack at all times.
The invention can be adapted to many forms and applications. The air spring, sandwiched between two members that are interlinked like links of a large chain, becomes an actuator that can be coupled directly between any two objects. It may be used in place of a hydraulic actuator, is lighter and less expensive than a hydraulic actuator and requires no maintenance.